MIT researchers bring in some new armor to help defense in the war on harmful bacteria.

Medical equipment related bacterial infections are a problem in hospitals worldwide. An estimated 100,000 people die each year to hospital-acquired infections. Various methods of preventing bacterial growth on medical tools have definitely helped to combat the problem, but it remains an issue worthy of research. Researchers at MIT may bring to bear another weapon for the war on harmful bacteria in the form of polymer films that measure only a few tens of nanometers thick.

Previously, research into preventing bacterial growth on surfaces focused on variables like surface roughness, surface charge and attraction or repulsion to water. The stiffness of the surface was generally overlooked. The MIT team has found this to be in error, and their research shows that growth can be inhibited, or fostered, by altering the mechanical stiffness of the surface in question.

While the group suffers no delusions that their film can prevent growth from happening, the ultimate goal is to help prevent as much as possible. The polyelectrolyte films, when combined with other already practiced methods of growth inhibition -- like impregnating the surface of an instrument with nanoscale metal particles to disrupt bacterial cell walls, or even simple antibacterial chemicals -- could serve to dramatically reduce the amount of biofilm growth.

The researchers found that they could control the stiffness of their nanofilm by adding alternating layers at different levels of pH. A more neutral pH creates a stiffer layer when hydrated by a near-neutral substance, like water, because the polymer chains more easily crosslink and suffer less swelling. Adding layers at a lower, or more acidic, pH creates a more compliant surface.

The group has already tested their films with three different strains of bacteria; two types of Escherichia coli, as well as the common Staphylococcus epidermidis. The experiments showed the same trend of growth inhibition based on surface stiffness. The trend may be explained by the relationship between pili, tiny projections from bacterial cell walls, and the stiffness of the surface they come into contact with. The pili may be encouraged to form more stable bonds to a stiffer surface.

The films could be used on just about any sort of medical device that comes in contact with the body, including implants like stents and pacemakers. Limiting the amount of bacteria that may find a home on such devices before they are inserted will help the immune system deal with infection by limiting the number of insurgents it needs to gun down.

On the flip side, the film could also be engineered to foster bacterial growth, aiding in applications that require such things, like medical testing and the production of the now famous or infamous alternative fuel ethanol.